A printed circuit board is made by printing circuit lines on an electrical insulating board using conductive material such as copper and indicates a circuit board in a state directly before electronic parts are mounted on. That is, a circuit board in which mounting locations of the electronic parts are fixed and in which circuit lines for connecting various kinds of electronic parts are printed on a planar surface.
In general, the printed circuit board is manufactured by photo-lithography process with high productivity and cheap manufacturing cost. There are several methods of manufacturing the printed circuit board using the photo-lithography process such as subtractive process and semi-additive process (SAP).
FIG. 1 illustrates an example of the subtractive process.
In detail, the subtractive process is performed by (a) forming a metal layer 2 on an insulating layer 1, (b) forming patterns 3 of photosensitive material by exposing and developing the photosensitive material after coating photosensitive material on the metal layer 2, (c) etching the patterns, and (d) forming a circuit pattern 4 by removing the photosensitive material 3.
FIG. 2 illustrates an example of the SAP.
In detail, the SAP is performed by (a) forming a seed layer 12 on an insulating layer 11, (b) patterning 13 by coating photosensitive material on the seed layer 12, (c) forming electroless copper plating layer 14, (d) removing the photosensitive material 13, and (e) removing the seed layer 12. In the SAP, as illustrated in FIG. 3, the circuit pattern 14 may be formed on a desired location with respect to the alignment.
However, since circuits of the printed circuit board manufactured by the subtractive process and the SAP do not have an even surface of the insulating layer, there is a limit of forming a fine pattern. Low illuminance of a surface including the insulating material is advantageous in order to form the fine pattern. However, in this case, contact between the insulating layer and the photosensitive material becomes poor and has a negative effect on forming a circuit due to delamination occurring during a series of processes of forming the circuit. When illuminance is high, contact between the photosensitive material and a base material is improved. However, since fine Cu may easily remain in rough insulating material during the process of removing a final seed layer after the plating and the delamination of photosensitive material, there is a strong possibility of electrical short. Since etchant permeates the under layer of the circuit and it makes forming the shape of the circuit difficult, the high illuminance has a negative effect on forming fine pattern with high reliability.
Therefore, in order to realize a fine pattern, a special method must be required because of the negative relationship between illuminance of the insulating material and the capability of realizing a fine pattern with reliability.
As a method of solving the limitation for the fine pattern, it is considered a method of embedding a circuit by forming a pattern shape of the circuit on a series of carrier substrate including a surface of a metal layer and an insulating layer for supporting the metal layer, by turning the carrier boards such that the circuit faces the insulating material, and by pressing the circuit.
FIG. 4 illustrates an example of a process of embedding a circuit pattern in the insulating layer.
The process is performed by (a) forming a carrier board 21 including a seed layer 22, (b) coating and patterning 23 a photosensitive material, (c) filling a metal material to form a circuit pattern 24, (d) removing the photosensitive material 23, (e) aligning the circuit pattern 24 to face the insulating layer 25 and laminating, (f) pressing the aligned circuit pattern, (g) removing the carrier board 21, and (h) removing the seed layer 22.